1. Field of the Invention
The present invention relates to an accumulator control method for controlling an accumulator connected to the oil hydraulic circuit of an injection molding machine.
2. Description of the Relevant Art:
In a conventional method for controlling an accumulator connected to the oil hydraulic circuit of an injection molding machine as disclosed in Japanese Patent Application Laid-Open (kokai) No. 5 (1993)-50483, the charge pressure of an accumulator is sensed by means of a pressure switch; when the charge pressure Pc of the accumulator reaches a lower limit Ld, a control valve is operated so as to charge the accumulator with hydraulic oil as shown in FIG. 6; and when the charge pressure Pc of the accumulator reaches an upper limit value Lu, the control valve is operated so as to terminate charging. Thus, the accumulator is always charged with hydraulic oil at a predetermined pressure or higher.
However, the above conventional method of controlling an accumulator involves the following problems.
First, since the accumulator is charged based on the charge pressure Pc sensed by the pressure switch, charge start points Sa, Sb, Sc, Sd, . . . and charge end points Ea, Eb, Ec, . . . appear at irregular intervals in corresponding molding cycles, as shown in FIG. 6. Accordingly, the charge pressures Pc in the respective steps of each molding cycle vary among molding cycles. As a result, molding cannot be performed stably with a high degree of reproducibility, and molding quality is impaired and variable.
Second, since the accumulator is charged through control that is performed based on a predetermined upper limit Lu of pressure and a predetermined lower limit Ld of pressure, the accumulator is often wastefully charged, resulting in an impairment of energy economy and economical efficiency.